CO2 in Aerobic, Anaerobic Composting

Composting is a common method for organic waste disposal. In composting, micro-organisms convert waste into useful products like fertilizer.

There are 2 kinds of composting: aerobic (with air) and anaerobic (without air). Although both break down organic matter, aerobic composting depends on micro-organisms that get oxygen from the air, whereas anaerobic composting depends on micro-organisms that get oxygen directly from the waste matter.

Aerobic Composting

The advantages of composting is that it naturally kills pathogens like E. coli, converts ammonia nitrogen to organic nitrogen and reduces the waste volume. The disadvantages of composting are the loss of some nutrients including nitrogen, the land area required for the composting, and odor. In addition, temperature, moisture content and aeration must be carefully monitored during decomposition to eliminate pathogens and completely convert the organic waste into compost.

While “compost piles” have been used by backyard gardeners for generations, some modern farms now use large-scale composting techniques in order to get rid of animal waste. One method for turning solid organic waste into compost is to use an ‘in-vessel’ composting technique. Basically a “scaled up” version of a hand-rotated yard composter, these large metal cylinders are slowly rotated as waste enters into one end and compost is extracted from the other. Using this method, the composter turns manure, litter, sour feed stuffs and even animal carcasses into compost in 4 days with minimal labor.

In aerobic composting, the more oxygen that is available, the more carbon dioxide (CO2) produced, the less methane (CH4), and the more complete the decomposition. As biological activity progresses, the oxygen concentration falls and CO2 concentration increases. While CO2 concentrations can vary, a sensor capable of measuring up to 30% CO2 like our K-33 ICB 30% CO2 Sensor should be used.

Anerobic Composting

As an alternative to aerobic composting, anaerobic composting is commonly used to treat human effluent and other livestock waste. Anaerobic digestion involves the degradation of organic waste under anaerobic conditions by microbial organisms to produce methane and inorganic solids. It has the advantage of being a highly efficient process, and can produce biogas for power generation or heating. In addition, the bio-solids remaining after the digester process can be sold as a high quality fertilizer.


In anaerobic composting, organic matter and water combine to generate CH4 and CO2. The difference is that it should primarily generate CH4, some CO2 and trace amounts of hydrogen sulfide (H2S), nitrogen and oxygen. Because CO2 levels in biogas can approach 40%, typically a 50-100% CO2 sensor should be used. For example, our 50% CO2 + 100% CH4 Sensor would work for this purpose.

Regardless of whether aerobic or anaerobic composting is used, CO2 level monitoring is critical for measuring the efficiency of the process.

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